1. Field of the Invention
The invention relates to nuclear spin tomography and, in particular, to medical instruments for examining human and animal bodies. Nuclear spin tomography is also known as magnetic resonance tomography, MRT for short.
MRT is an image-generating method based on the physical phenomenon of nuclear spin resonance. An object to be examined is subjected to a strong magnetic field. This causes an alignment of previously statistically distributed nuclear spins of the individual atoms. Excitement with high-frequency energy from outside causes measurable vibrations. In order now to render possible a spatial localization, magnetic fields which are inhomogeneous along the three spatial axes are generated using gradient coils in the magnetic field. Transmitting coils are provided for emitting the high-frequency excitation energy. A reception of excited oscillations is effected with receiving coils. Transmitting coils and receiving coils are frequently combined with each other. In the following, these coils are also referred to as HF coils, because they serve for coupling-in or coupling-out high-frequency signals.
This non-invasive image-generating method makes it possible to obtain images of sections through a human or animal body along any desired axes.
2. Description of the Prior Art
Examples of transmitting and receiving coils are disclosed in U.S. Pat. No. 4,887,039. There a plurality of parallel conductors which are connected to each other via coupling capacitors are mounted on a cylindrical support. Feeding is effected by means of symmetrical conductors or coaxial cables. So-called phased-array arrangements, as shown in FIG. 4 of this Patent Specification, are employed in order to achieve higher resolutions. For this, a plurality of independent coils having independent receiver inputs are connected for separate evaluation of the signals.
The construction of coils of this kind is very complex, and the manufacturing costs are therefore relatively high. In coil arrangements of the future, an increasing number of coils will have to be provided, whilst the higher resolution will cause even greater demands to be made on the mechanical tolerances.